1. Field of the Invention
This invention relates to an automatic picture quality adjustment apparatus for use in a television receiver or the like. More particularly, it relates to an apparatus in which input video signals are subjected to the operation of level conversion for adjustment of the picture quality, in a manner such that the picture quality of an image on a screen surface or raster, such as brightness, contrast, color saturation or color hue, may be automatically adjusted.
2. Description of Related Art
In general, in a video signal processing system of a television receiver or a monitor receiver, the picture quality adjustment apparatus for adjusting the picture quality, such as the luminosity or the brightness, the contrast, the color saturation or the color hue, is used to obtain the correct picture quality or a picture quality which is suited to the desires of the individual users.
With such picture adjustment apparatus, the input video signals are subjected to a level conversion operation for picture quality adjustment, such as by changing the amplification factor or the phase of the luminance component and/or color components of the input video signals, so as to adjust the picture quality, such as brightness or contrast. Heretofore, the parameters used for the operation of conversion for such picture quality adjustment are manually set with a setting switch, or are set to a standard value which is preset at the factory, by an automatic switch, such that the picture quality of the entire screen surface or raster is adjusted uniformly by the thus set parameters.
With the above described conventional picture quality adjustment apparatus, the picture quality is uniformly adjusted over the entire screen surface or raster. Thus, although it is possible with the conventional picture quality adjustment apparatus to realize a balanced adjustment of the entire picture quality of the screen surface or raster a proper picture quality is not realized in this case as for the picture quality of detail areas of the screen surface or raster.
For example, if an unusually white-tinted small region exists on the screen surface, such as a telop of a title, for example, which is superimposed in white in a zone of the screen surface, the white-tinted region will be over pronounced in contrast, if a proper contrast is obtained in the remaining regions, with the result that the title or the like may occasionally be barely legible. Conversely, if the contrast of the white-tinted region is weakened so as to render the title more legible, the contrast of the remaining regions of the picture surface are also weakened, with the result that the image displayed on the screen is poor.
On the other hand, a so-called two-image television system has been developed, in which a subsidiary image is superimposed on the main image and which uses digital signal processing of the video signals. However, if the conventional picture quality adjustment apparatus is used in the two-image television system, since both the main image and the subsidiary image will be subjected to the same picture quality adjustment operation, when the main image is light and the subsidiary image is rather dark, and if the lightness level is lowered to obtain the desired level of lightness for the main image, the subsidiary image will be too dark and hence it is not possible to obtain a proper picture quality for the subsidiary image.